Liquid purification or separation – Plural chambers with movement of granules therebetween
Patent
1995-09-25
1998-05-26
Popovics, Robert
Liquid purification or separation
Plural chambers with movement of granules therebetween
210268, 210269, 210274, 210792, B01D 2428
Patent
active
057559597
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to methods and devices for achieving a uniformly distributed flow of suspension through a granular filter bed in a continuously working filter. The invention therewith achieves optimization of the capacity of the filter.
By a continuously working granular filter is meant here and in the following any type of filter in which filter medium is removed continuously from the bottom of the filter bed, washed and then returned to the upper side of the filter bed as suspension passes through the filter bed and cleaned thereby. An example of one such filter is described in Swedish Patent Specification 7602999-0. The particulate filter medium, normally sand, is enclosed in a circular or polygonal container which has a conical or pyramidal bottom. The suspension or emulsion to be treated is taken in through an inlet at the bottom of the filter bed. The suspension or emulsion flows into the filter bed through a number of pipes whose orifices are located beneath a roof or ceiling structure. The orifice of a lifting device, conveniently a mammoth pump or air lift, is placed in the lowermost part of the conical bottom. Such a pump uses air as the transporting medium. The pump pipe or tube extends up through the filter bed to a washing device, from which washed sand is distributed over the upper side of the filter bed. The incoming suspension thus flows in countercurrent to the filter medium outwards through the filter bed towards progressively more cleaner filter medium and leaves the filter through an outlet, via a weir means. A cone is positioned in the lower part of the filter bed with the apex of the cone facing upwards, so as to contribute to a desired flow profile of the filter medium. This cone is referred to in the following as a guide one.
The known technique includes several solutions to the problem of introducing the suspension into the filter bed in a manner which will result in a uniformly distributed flow over the filter area. Known to the art are devices which distribute the suspension in different directions out towards the periphery with the aid of radially extending arms. Other inlets take place around the outer wall and also further in towards the center. A common feature of all solutions is an assumption that precisely this or that solution will provide a uniformly distributed flow throughout the whole of the filter. This assumption remains hypothetical unless it can be proved to be true with the aid of concrete measurements. The difficulties in taking such measurements have evidently presented such a large obstacle to obtaining a true picture of prevailing realities that the matter has quite simply been ignored.
SUMMARY OF THE INVENTION
The present invention is based on a large number of measurements of the flow conditions that were taken at a plurality of measuring points distributed both radially and axially in the filter bed. The result of these measurements was surprising. Two very essential observations could be made. Firstly, it was found that the flows had a very strong tendency to curve out towards the outer surface of the filter immediately downstream of the inlet. Those inlet devices that were placed adjacent the outer surface and also slightly inwards of the outer surface produced an equally as large flow within the 30% of the total area that lay proximal to the outer surface as in the whole of the remainder of the filter. In hydro-mechanical terms, it is possible that this was due to a smaller grain density of the filter material around the outer surface or mantle of the filter bed. Secondly, it was found that the flatness of the upper surface of the filter bed had a strong influence on the flows in an area located some decimeters beneath the surface. The upper surface of the filter bed had an undulating configuration, presenting ridges or crests, and the liquid flows deviated beneath parts of the upper surface and were directed towards the nearest troughs of the undulations. The important conclusion that can be drawn from thes
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Hagrot Magnus
Jonsson Kurt
Lenvik Lennart
Oskarsson Jonas
Nordic Water Products AB
Popovics Robert
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